One of them is being able to override `setattr` and `getattr` at runtime in Python. It can be pretty tricky to prove it can't happen, so (unless you have optimi

One of them is being able to override `setattr` and `getattr` at runtime in Python. It can be pretty tricky to prove it can't happen, so (unless you have optimistic and pessimistic codepaths) you get into a situation where every attribute lookup makes indirect function calls and hash-table lookups.